The present invention relates to a control apparatus of a variable valve timing system for an internal combustion engine, and particularly to techniques for controlling a rate of change in an angular phase of a camshaft relative to a crankshaft in a variable valve timing system capable of variably controlling an engine valve timing by varying the angular phase of the camshaft relative to the crankshaft.
A variable valve timing system generally uses a return spring for return to an initial position that there is no angular phase difference between the camshaft and the crankshaft. The initial position is determined by way of collision-contact with a stopper during the return to the initial position. For instance, in case of a hydraulically-operated variable valve timing system, in order to for the variable valve timing system to returning to its initial position, a variable valve timing controller (VTC controller) generates an inactive signal. Owing to the output of the inactive signal, the hydraulic pressure is released and thus the IVC system returns to the initial position. In this case, there is a time delay until the hydraulic pressure reduces to below a predetermined level. In other words, the returning speed to the initial position is slow. Such a slow return is often called xe2x80x9csoft-landingxe2x80x9d. In contrast, in case of a variable valve timing system that uses an electromagnetic brake controlled by an electronic control module and capable of varying the angular phase of the camshaft to the crankshaft by way of friction brake, for return-to-initial-position, first, a VTC controller generates an inactive signal. The electromagnetic brake is deactivated, and thus the frictional braking force rapidly drops to zero. As a result, the VTC system returns to the initial position for a brief moment by way of the spring bias of the return spring. In this case, there is no problem of an undesirable slow return to the initial position. However, there is another problem of noises created by collision-contact with the stopper. One such variable valve timing system with an electromagnetic brake has been disclosed in Japanese Patent Provisional Publication No. 10-153105.
Accordingly, it is an object of the invention to provide a control apparatus of a variable valve timing system, which avoids the aforementioned disadvantages.
It is another object of the invention to provide a control apparatus of a variable valve timing system, which is capable of optimally controlling a rate of change in an angular phase of a camshaft relative to a crankshaft, for the same control condition, namely the same controlled range and the same control responsiveness, thereby reducing noises created by collision-contact with a stopper and ensuring the increased life of the stopper.
In order to accomplish the aforementioned and other objects of the present invention, a control apparatus of a variable valve timing system for an internal combustion engine, comprises a sensor that detects an angular phase of a camshaft relative to a crankshaft, a return spring that returns the angular phase of the camshaft to an initial position, and an electronic control unit configured to be electronically connected to the variable valve timing system to variably control a valve timing by changing the angular phase of the camshaft against a spring bias of the return spring and execute a revertive control by which the angular phase of the camshaft is returned to the initial position, the electronic control unit comprising a processor programmed to perform the following: (a) executing a feedback control that temporarily halts the angular phase of the camshaft at a predetermined position, which is phase-changed by a predetermined phase angle from the initial position, during the revertive control, and (b) switching to a feedforward control after the feedback control, so as to return the angular phase of the camshaft to the initial position.
According to another aspect of the invention, a variable valve timing system for an internal combustion engine comprises a sensor that detects an angular phase of a camshaft relative to a crankshaft, and an electronic control unit capable of performing a revertive control by which the angular phase of the camshaft is returned to an initial position with a specified control pattern, the electronic control unit comprising a processor programmed to perform the following: (a) switching an operating mode of the variable valve timing system from a feedback control to a feedforward control at a predetermined position, which is phase-changed by a predetermined phase angle from the initial position, during the revertive control.
According to a further aspect of the invention, a control apparatus of a variable valve timing system for an internal combustion engine, comprises a sensing means for detecting an angular phase of a camshaft relative to a crankshaft, a return spring for returning the angular phase of the camshaft to an initial position, and an electronic control unit configured to be electronically connected to the variable valve timing system to variably control a valve timing by changing the angular phase of the camshaft against a spring bias of the return spring and execute a revertive control by which the angular phase of the camshaft is returned to the initial position, the electronic control unit comprising (a) a feedback control means for executing a feedback control that temporarily halts the angular phase of the camshaft at a predetermined position, which is phase-changed by a predetermined phase angle from the initial position, during the revertive control that the angular phase of the camshaft is adjusted toward the predetermined position, and (b) a feedforward control means for initiating a feedforward control after the feedback control, so as to return the angular phase of the camshaft from the predetermined position to the initial position.
According to a still further aspect of the invention, a soft-landing revertive control method of returning an actual angular phase of a camshaft relative to a crankshaft to an initial position by controlling the actual angular phase of the camshaft in a variable valve timing system for an internal combustion engine, employing a return spring creating a spring bias acting in a direction that returns the actual angular phase of the camshaft to an initial position and an electromagnetic brake creating an electromagnetic force acting against the spring bias, the method comprises de-energizing the electromagnetic brake, calculating a target angular phase of the camshaft based on engine operating conditions, comparing the target angular phase to a predetermined position, which is phase-changed by a predetermined phase angle from the initial position, comparing the actual angular phase to the predetermined position, executing a feedback control that temporarily halts the actual angular phase of the camshaft at the predetermined position after the target angular phase reaches the predetermined position and the actual angular phase also reaches the predetermined position, and switching an operating mode of the variable valve timing system from the feedback control to a feedforward control after the feedback control has been continuously executed for a predetermined time period from a time when the actual angular phase has reached the predetermined position.
The other objects and features of this invention will become understood from the following description with reference to the accompanying drawings.